Applications are known in which hoses that are reinforced with armor layers that consist of steel wires are used to transport fluids, particularly hydrocarbons. In certain cases, these hoses are placed under conditions where they are subjected to a corrosive environment, for example, in the presence of acidic fluids that contain sulfurated products. Also, in case where such hoses are placed in very deep water, more and more they need to have very high mechanical performance levels in terms of resistance to internal pressure, to axial load, and to external pressure resulting from the great depth of immersion.
In the hoses, whereby sealing is ensured by one or more polymer sheaths, mechanical resistance to internal and external pressure and to external mechanical stresses is provided by one or more armor layers that consist of wires or steel sections that have a specific profile.
Generally, the hose comprises at least one of the following armor layers: a casing for resistance to external pressure that is made of wires or sections that are arranged at an angle of close to 90.degree. relative to the axis, a layer for resistance to internal pressure (called an arch) that is arranged at an angle of greater than 55.degree., with the elongated elements of the casing and the arch preferably being wires that can be laced, and at least one tensile-strength armor layer that is wound at an angle of less than 55.degree.. According to another method, the arch and the traction armor are replaced by two symmetrical armor layers that are wound at an angle of about 55.degree., or by two pairs of layers that are wound at 55.degree., or else by a set of at least two layers, with the winding angle of at least one layer being less than 55.degree. and the winding angle of at least one another layer being greater than 55.degree.. The steel of the wires that comprise the reinforcements is to be selected in such a way that these wires, taking into account their section, provide the mechanical strength that is necessary in service at the same time that they withstand corrosion, in particular in some cases in the presence of H.sub.2 S.
These steel wires, which are generally shaped by rolling or hot or cold drawing, can have different profiles, i.e., straight sections: approximately flat or a flat surface, shaped in a U, T, or Z, with or without means for hooking to an adjacent wire, or circular.
In the case where these products are used in the presence of acid gas, basically H.sub.2 S and CO.sub.2, in addition to generalized corrosion, problems can arise that are connected with the penetration of hydrogen into the steel. Actually, H.sub.2 S (or rather the HS.sup.- ion) is a substance that inhibits the recombination of hydrogen atoms that are produced by reduction of protons at the surface of the steel. These hydrogen atoms are introduced inside the metal and recombine there, thus giving rise to two types of deteriorations:
bubbles under the surface of the steel ("hydrogen blistering," we then speak of "blisters"), or internal cracking (called stepwise cracking) can appear in the absence of stress and can be aggravated in the presence of residual stress, PA1 an embrittlement that results in delayed ruptures in the case where the steel is put under stress (hydrogen stress corrosion). PA1 from 0.05% to 0.8% of C, PA1 from 0.4% to 1.5% of Mn, preferably less than 1% of Mn, PA1 from 0 to 2.5% of Cr, between 0.25 and 1.3%, PA1 from 0.1% to 0.6% of Si, PA1 from 0 to 1% of Mo, PA1 at most 0.50% of Ni, PA1 at most 0.02% of S and P, and preferably S less than or equal to 0.005%, PA1 optionally with, in addition to the action of Si, deoxidizing with aluminum or silico-calcium, PA1 a thermal treatment that comprises at least one quenching operation is carried out on the shaping wire, optionally under conditions that are adjusted to obtain an HRC hardness that is greater than or equal to 32, and preferably greater than or equal to 35 and can advantageously reach or exceed 50, PA1 the structure of the steel of the shaping wire that is thus obtained is predominantly martensite-bainite. PA1 between 0.1% and 2.5% of Cr, preferably between 0.25 and 1.3%, PA1 between 0.1% and 1% of Mo, PA1 with the steel thus being of the low-alloyed type and being consistent with grades that are common in the industry and are of relatively limited cost. PA1 in a bath between 300 and 550.degree. C., with the speed being matched to the section of the wire to obtain a hardness, according to this invention, of greater than or equal to 32 HRC, PA1 in a coil in a furnace between 150 and 300.degree. C. PA1 Wire shaping by hot rolling: PA1 from 0.05% to 0.8% of C, PA1 from 0.4% to 1.5% of Mn, preferably less than 1% of Mn, PA1 from 0 to 2.5% of Cr, preferably between 0.25 and 1.3%, PA1 from 0.1% to 0.6% of Si, PA1 from 0 to 1% of Mo, PA1 at most 0.50% of Ni, PA1 at most 0.02% of S and P, and preferably S less than or equal to 0.005%.
NACE standards have been provided for evaluating the suitability of a steel structural element for use in the presence of H.sub.2 S. The steels should undergo a test on a representative specimen, under stress in an H.sub.2 S environment with a pH of 2.8 to 3.4 (NACE Test Method TM 0177 pertaining to the results of stress cracking, commonly referred to as "Sulfide Stress Corrosion Cracking" or SSCC), in order for them to be considered usable in the production of metal structures that have to withstand the effects of corrosion under stress in the presence of H.sub.2 S.
Another NACE standard (TM 0284) relates to the effects of cracking that are induced by hydrogen, commonly referred to as "Hydrogen-Induced Cracking" or HIC. The test procedure that is recommended by the above standard consists in exposing specimens, without stress, to a sea water solution that is saturated with H.sub.2 S, at ambient temperature and ambient pressure, at a pH of between 4.8 and 5.4. The procedure then calls for carrying out metallographic examinations to quantify the cracking of the specimens or to demonstrate the absence of cracking. An additional criterion for evaluating specimen damage can be the determination of mechanical characteristics after an HIC test. This criterion does not appear in NACE standard TM 0284. Applicants have thus been led to define an additional evaluation method that consists in carrying out tensile strength tests on specimens to determine the mechanical characteristics after HIC and to compare these results with the mechanical characteristics before HIC. This method has proved to be particularly advantageous in the case of reinforcement wires that are the object by this invention, with these wires being subjected to conditions of uniaxial longitudinal stresses, by comparison with the walls of steel tubes, which tubes constitute the main application of the NACE standards. Another supplementary method consists in comparing necking loss values Z (%) before and after the HIC test, whereby the difference should be relatively small and preferably less than 30%.
With the conditions of drilling for underwater deposits having become tougher and tougher over time, it recently appeared that the qualification of the materials for their use in the presence of H.sub.2 S should target the case of a more acidic environment, where the pH can be as low as about 3. It was thus specified that in certain cases the tests according to NACE standard TM 0284 should be carried out in a solution that is saturated with H.sub.2 S that has a pH of, for example, 3 or 2.8, similar to the solution that is defined by NACE standard TM 0177, and no longer with a pH that is at least equal to 4.8.
According to the techniques that are currently known, the reinforcement wires of hoses, in particular for the case where fluids that contain H.sub.2 S are being transported, are made with soft or medium-hard carbon-manganese steels (0.15 to 0.50% carbon) that have a ferrite-pearlite structure to which is applied, after the hot-rolled rods are cold-shaped, a suitable thermal annealing treatment to bring the hardness to the accepted value, if necessary.
NACE standard 0175 defines that such carbon-manganese steels are compatible with an H.sub.2 S environment if they have a hardness of less than or equal to 22 HRC. It has thus been verified that reinforcement wires, as described above, made of carbon-manganese steel and having a ferrite-pearlite structure, can be produced by cold shaping, followed by annealing to meet the traditional NACE criteria. A process that is described in document FR-A-2661194 which makes it possible to obtain steel with a hardness of more than 22 HRC and is compatible with H.sub.2 S according to NACE standards TM 0177 and TM 0284 is known, with the solution that is used for the tests according to TM 0284 having a pH of between 4.8 and 5.4.
On the other hand, it has been found that the carbon steels with a ferrite-pearlite structure are incapable of satisfactorily withstanding the HIC tests that are carried out according to the procedure of standard TM 0284 when these tests are carried out in a more acidic environment, for example with a pH on the order of 3, which corresponds to conditions now being encountered in certain cases in petroleum deposit mining. These unacceptable results were obtained even in the case where the final thermal treatment is more intense, so as to obtain an HRC hardness that is less than 22 HRC.
Therefore, in order to produce hose reinforcement wires, there is a need for a steel that, on the one hand, is compatible with H.sub.2 S under the new conditions that are described above and that, on the other hand, have a composition and a process of production that are relatively standard and fairly low-tech in order to keep production costs sufficiently low.
Furthermore, the steels and the production processes that are used to produce hose reinforcement wires should be such that the shaping wire can be produced in very long continuous lengths, on the order of several hundreds of meters or several kilometers. The wire that is thus produced is wound in coils with a view to its later use to produce hose reinforcement layers. In addition, despite the very large unit lengths of the wires that are thus produced, it is important that they can be connected by welding during the reinforcement operation in the course of the production of the hose. To recreate, in the welding zone, the specified properties of the steel, in particular the resistance to H.sub.2 S, thermal treatment is to be provided after welding.
In the case where compatibility with H.sub.2 S is not required (production of "sweet crude"), carbon steels in the cold-shaped raw state that also have a ferrite-pearlite structure but have considerably higher mechanical strength and hardness values are commonly used. It has been found, nevertheless, that increasing mechanical strength beyond certain limits causes such steels to have inadequate ductility, taking into account the preshaping and reinforcement operations that have to be carried out with the reinforcement wire.